This invention relates to the use of photoiniators. More particularly, it relates to the stabilization of photoinitiators useful in processes for making ophthalmic lenses.
Ophthalmic lenses such as contact lenses are often made in processes that employ photoinitiated polymerization reactions. UV and visible radiation are most frequently used to initiate cure in these reactions. It is often desirable to prepare a mixture of materials together with an initiator or initiator system (where initiation involves more than one component) and other additives that will ultimately form the lens upon completion of the reactions. These types of mixtures are referred to as the xe2x80x9cmonomer mixxe2x80x9d in this context. Stability of the initiator can be a crucial factor in the working time and shelf life of the monomer mix. Increasing the working time of the monomer mix is desirable since it reduces the need for preparation of starting materials and the possibility of introducing lot to lot and intra-lot variations in lens production. Acylphosphines are an interesting and useful class of initiators for free radical polymerations of the type frequently used to made ophthalmic lenses. Reaction mechanisms for many of these materials are described in Reaction Mechanism of Monoacyl- and Bisacyiphoine Oxide Photoinitiators Studied by 31P, 13C-, and 1H-CIDNP and ESR, Ursul Kolczak, Gunther Rise, Kurt Dietliker, and Jacob Wirz, 118 J. Am. Chem. Soc., 6477 (1996). Bisacylphosphines and their use are further described in U.S. Pat. No. 5,534,559 and JP-A-8-259642 incorporated herein by reference.
Unfortunately, this class of compounds tends to be unstable in a variety of environments lessening its potential as an active initiator. EP 849,296 proposes a method of stabilizing bisacylphosphine initiators used in the production of urethane (meth)acrylate polymers used for coatings. The method involves combining the monomer components together with the initiator in the presence of a tertiary amine and in the absence of a tin component. Japanese patents JP-A-4-6125; JP-A-296315; JP-A8-127630 propose similar methods of stabilizing monoacylphospine photoinitiators in the presence of a tin compound used as a polymerization catalyst.
Unfortunately, these solutions are not desirable when applied to monomer mixes used to make ophthalmic lenses because of the potentially deleterious effect they may have on various components of the monomer mix. This is particularly true where the monomer mix is used to make silicone hydrogel lenses.
A new method for stabilizing acylphosphine initiators is desirable.
The invention is a stable monomer mix for making ophthalmic lenses. The stable monomer mix is made by admixing a monomer mixture, an initiator, and an acid.
In another aspect of the invention a silicone hydrogel monomer formulation is made by admixing a silicone hydrogel forming mixture, an initiator, and an acid.
In yet another aspect of the invention, a method of stabilizing an initiator system comprises lowering the pH of the initiator system.
In yet another aspect of the invention, a process for stabilizing a silicone hydrogel monomer formulation in an admixture of a reactive silicone macromer and a photoiniator comprises admixing an acid with the admixture of macromer and photoinitiator.
The initiators of this invention are those having the following structure: 
wherein, R1, R2, and R3 are each independently H or a C1-12 substituted or unsubstituted alkyl cycloalkyl, or aromatic moiety provided that at least one of R1, R2 and R3 has the following structure: 
and is attached to the P at the acyl carbon, and wherein, R4-R8 are independently, H or a C1-3 substituted or unsubstituted alkyl or alkoxy moiety.
In each case, where an R1-R8 group is substituted, the substituent can comprise a hydroxy or C1-4 alkyl alkoxy, alkenyl, or alkynyl group. Substitution with hetero atoms such as nitrogen, sulfur, and halo atoms is possible but is not favored.
It is preferred that R1 and R2 are both Structure II moieties with R4 and R8 substituents. It is most preferred that R4 and R8 are methoxy groups. It is further preferred in this embodiment that R3 is a C1-10 alkyl alkoxy, or alkenyl group substituted with C1-2 alkyl groups; most preferably a substituted pentyl group.
In the most preferred embodiment, R1 and R2 are both Structure II moieties with R4 and R8 being methoxy groups; R1 is a trimethyl pentyl group. Thus, the most preferred embodiment has the following structure: 
Theses initiators can be used alone or in combination with other initiators such as benzoin methyl ether, 1-hydroxycyclohexyl phenyl ketone, Irgacure 1850 brand photoinitiator, 1-hydroxy cyclohexyl phenyl ketone (commercially available as xe2x80x9cIrgacure 184xe2x80x9d); 2-benzyl-2-n-dimethylamino-1-(4-morpholinophenyl)-i-butanone (commercially available as xe2x80x9cIrgacure 369xe2x80x9d); 1-hydroxycyclohexyl phenyl ketone (50% by weight) plus benzophenone(commercially available as xe2x80x9cIrgacure 500xe2x80x9d); 4-(2-hydroxyethoxy) phenyl-(2-hydroxy propyl)ketone (commercially available as xe2x80x9cIrgacure 2959xe2x80x9d); 2,4,6-Trimethyl benzoyl diphenyl phosphineoxide (TPO) (50% by weight) plus 2-hydroxy-2-methyl-1-phenyl-propan-1-one (HMPP) (50% by weight) (commercially available as xe2x80x9cDarocur 4265xe2x80x9d); 2,2-dimethoxy-2-phenylacetophenone (BDK) (commercially available as xe2x80x9cIrgacure 651xe2x80x9d); bis (n1-2,4-cyclopentadien-1-yl), bis (2,6-difluoro-3-(IH-pyrrol-1-yl)phenyl) Titanium (CGI-784); 2-methyl-1-(4-(methylthio)phenyl)-2-morpholino propan-1-one (MAP) (commercially available as xe2x80x9cIrgacure 907xe2x80x9d); 2-hydroxy-2-methyl-1-phenyl-propan-1-one (HMPP) (commercially available as xe2x80x9cDarocur 1173xe2x80x9d); or mixtures thereof. Mixtures that include a UV and visible light initiator system are preferred as they permit more flexible use of UV blockers in the monomer mix.
The stabilizers useful in this invention are acids. These are preferably weak organic acids but may include strong inorganic acids as well as Lewis acids. Additionally, precursors capable of generating acids in the reaction mixture can also be used. The most preferred acids are acetic acid, formic acid, propionic acid, and acrylic acid.
The inorganic acids include, for example, hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, hydroiodic acid, hydrofluoric acid, sulfurous acid, nitric acid, nitrous acid, phosphorous acid, perchloric acid, chloric acid, chlorous acid, iodic acid, bromic acid, arsenic acid, carbonic acid, selenium hydride, tellurium hydride, phosphonic acid, hypophosphoric acid, diphosphonic acid, pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid, selenic acid, selenious acid, telluric acid, tellurous acid, arsenious acid, antimonic acid, antimonous acid, borofluoric acid, etc.
The organic acids include, for example, the sulfonic acids such as hydroxymethanesulfonic acid, trifluoromethanesulfonic acid, beta-bromoethanesulfonic acid, allylsulfonic acid, 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid, D-10-camphorsulfonic acid, benzenesulfonic acid, m-nitrobenzenesulfonic acid, m-benzenedisulfonic acid, methanesulfonic acid, ethanesulfonic acid, 2-hydroxyethanesulfonic acid, 2-(cyclohexenylamino)methanesulfonic acid, (3-cyclohexenylamino)methanesulfonic acid, p-ethylbenzenesulfonic acid, alpha-naphthalenesulfonic acid, beta-naphthalenesulfonic acid, p-toluenesulfonic acid, p-chloromethylbenzenesulfonic acid, p-phenolsulfonic acid, 2-pyridylhydroxymethanesulfonic acid, 2,6-naphthalenedisulfonic acid, etc.; the organic sulfinic acids such as benzenesulfinic acid, p-toluenesuifinic acid, etc.; the organic phosphoric acids such as phenylphosphonous acid, butyphosphonous acid, methylphosphonous acid, dibenzenephosphinic acid, dibutylphosphinic acid, benzenephosphonic acid, methylphosphonic acid, phenylphosphinic acid, methylphosphinic acid, dibenzenethiophosphinic acid, dibutylthiophosphinic acid, benzenethiophosphonic acid, methylthiophosphonic acid, phenylthiophosphinic acid, methylthiophosphinic acid, benzenethiophosphonous acid, dibutylthiophosphonous acid, diethyl dithiophosphate, alpha-hydroxybenzylphosphonous acid, toluenephosphonous acid, etc.; the substituted or non-substituted aliphatic carboxylic acids include for example mandelic acid, acetic acid, lactic acid, ascorbic acid, phenylacetic acid, bromoacetic acid, trichloroacetic acid, chlorodifluoroacetic acid, thioacetic acid, glycolacetic acid, glyoxylic acid, acrylic acid, beta chloroacrylic acid, cyanoacetic acid, ethoxyacetic acid, beta-chloropropionic acid, perfluoropropionic acid, propiolic acid, n-butyric acid, isobutyric acid, alpha-hydroxyisobutyric acid, crotonic acid, mucochloric acid, cyclopropanecarboxylic acid, isovaleric acid, 1-methylcyclopropanecarboxylic acid, 1-cyanocyclopropanecarboxylic acid, cyclobutanecarboxylic acid, cyclopentanecarboxylic acid, 2-ketobutyric acid, levulinic acid, pivalic acid, tert-butylacetic acid, coumarinic acid, 3-cyclohexenecarboxylic acid, beta-2-furylacrylic acid, 3-pyridylacetic acid, phenylthioacetic acid, m-chlorophenylacetic acid, o-nitrophenylacetic acid, p-fluorophenylacetic acid, o-hydroxyphenylacetic acid, phenoxyacetic acid, o-chlorophenoxyacetic acid, 2,4-dichlorophenoxyacetic acid, 2,4,5-richlorophenoxyacetic acid, cyclohexylacetic acid, 1-methyl-1-cyclohexanecarboxylic acid, 6-acetamidohexanoic acid, heptylic acid, dl-terebic acid, benzoylformic acid, cinnamic acid, o-chlorocinnamic acid, 2,4-dichlorociniumic acid, m-nitrocinnamic acid, o-hydroxycinnamic acid, d-2-phenoxypropionic acid, 3-phenoxypropionic acid, 3-phenylpropionic acid, 3-(p-hydroxyphenyl)propionic acid, 2-(2,4,5-trichlorophenoxy)propionic acid, 4-methoxyphenylacetic acid, p-chloro-2-methylphenylacetic acid, 3,4-methylenedioxyphenylacetic acid, 4-chloro-2-methylphenoxyacetic acid, m-tolylacetic acid, alpha, alpha, alpha-trifluoro-m-tolylacetic acid, p-hydroxyphenylpyruvic acid, alpha-cyanocinnamic acid, p-methoxycinnamic acid, m-trifluoromethylcinnamic acid, 3,4-methylenedioxycinnamic acid 3,4 dimethoxyphenylacetic acid, (xe2x88x92)-alpha-methoxy-alpha-trifluoromethylphenylacetic acid, 1,4-benzdioxane-6-acetic acid, 3-phenyl-n-butyric acid, 1-phenyl-1-cyclopropanecarboxylic acid, 2-(p-methoxyphenyl)-acetylene-1-carboxylic acid, 3-benzoylpropionic acid, 2-(p-chlorophenoxy)-2-methylpropionic acid, alpha-naphthylacctic acid, beta-naphthoxyacetic acid, 3,4,5-trimethoxyphenylacetic acid, diphenylacetic acid, bis(p-chlorophenyl)acetic acid, 1-menthoxyacetic acid, diphenyleneacetic acid, 1-phenylcyclopentanecarboxylic acid, 1-(p-chlorophenyl)-1-cyclopentanecarboxylic acid, dl-3-camphorcarboxylic acid, palmitic acid, stearic acid, benzilic acid, desoxycholic acid, linolic acid, oleic acid, alpha-acetamidocinnamic acid, etc.; the aromatic carboxylic acids include for example benzoic acid, salicylic acid, o-toluic acid, alpha, alpha, alpha-trifluoro-m-toluic acid, p-ethylbenzoic acid, 2,6-dimethylbenzoic acid, 2,4,6-trimethylbenzoic acid, p-tertbutylbenzoic acid, p-bromomethylbenzoic acid, 2-biphenylcarboxylic acid, 4,4xe2x80x2-methylenebis(3-hydroxy-beta-naphthoic acid), alpha-naphthoic acid, p-benzoylbenzoic acid, phthalamic acid, o-phthalaldehydic acid, m-nitrobenzoic acid, 3,4-dinitrobenzoic acid, m-cyanobenzoic acid, thiosalicylic acid, gallic acid, m-hydroxybenzoic acid, 2,3-dihydroxybenzoic acid, 1-hydroxy-2-naphthoic acid, o-anisic acid, 3,4-dimethoxybenzoic acid, 4-hydroxy-3-methoxybenzoic acid, 4-hydroxy-3,5-dimethoxybenzoic acid, 4-n-butoxybenzoic acid, 3-phenoxybenzoic acid, piperonylic acid, o-acetamidobenzoic acid, p-chlorobenzoic acid, 3,5-dichlorobenzoic acid, o-fluorobenzoic acid, m-fluorobenzoic acid, 2,6-difluorobenzoic acid, 2,6-dichlorobenzoic acid, 2,3,5-triiodobenzoic acid, 4-chlorosalicylic acid, 3-nitrosalicylic acid, 5-bromosalicylic acid, 2-chloro-3-nitrobenzoic acid, 3-chloro-4-hydroxybenzoic acid, 3,5-dichloro-4-hydroxybenzoic acid, 3-chloro-4-methylbenzoic acid, 3-methoxy-4-nitrobenzoic acid, 3-methoxy-4-hydroxybenzoic acid, 3-methoxy-4-methylbenzoic acid, 3-methyl-2-nitrobenzoic acid, 3-hydroxy-4-nitrobenzoic acid, 3,5-di-tert-butyl-4-hydroxybenzoic acid, o-thymotinic acid, etc.; the heteroaromatic carboxylic acids include for example N-methylpyrrole-2-carboxylic acid, 2-furancarboxylic acid, 5-bromo-2-furancarboxylic acid, pyrrole-2-carboxylic acid, 3-furancarboxylic acid, nicotinic acid, isonicotinic acid, citrainic acid, alpha-picolinic acid, etc.; the substituted or non-substituted aliphatic polyhydric carboxylic acids include for example succinic acid, fumaric acid, maleic acid, malic acid, tartaric acid, citric acid, oxalic acid, malonic acid, ethylmalonic acid, hydroxymalonic acid, methylsuccinic acid, 2-methyl-2-phenylsuccmnic acid, 2-ethyl-2-methylsuccinic acid, 2-isopropylsuccinic acid, bromosuccinic acid, 2,3-dibromosuccinic acid, alpha-ketoglutaric acid, 3-ethyl-3-methylglutaric acid, glutaconic acid, itaconic acid, mesaconic acid, citraconic acid, adipic acid, camphoric acid, diglycollic acid, acetylenedicarboxylic acid, dimethylcyclopropanedicarboxylic acid, etc.; the aromatic dicarboxylic acids include for example phthalic acid, isophthalic acid, terephthalic acid, homophthalic acid, 3-nitrophthalic acid, 4-hydroxyisophthalic acid, tetrachlorophthalic acid tetrachloroterephthalic acid, nitroterephthalic acid, pyrazine-2,3-dicarboxylic acid, o-phenylenediacetic acid, 5,5xe2x80x2-methylenedisalicylic acid, etc.; the phenols include for example picric acid, 2,4-dinitrophenol, 2,6-dinitrophenol, 2,6-diiodo-4-nitrophenol, 2,6-dichloro-4-nitrophenol, 2,5-dichloro-4-nitrophenol, 2,6-dibromo-4-nitrophenol, 2-bromo-4-chloro-6-nitrophenol, 2-dichloro-6-nitrophenol, etc.; and the substituted or non-substituted dithiocarbamic acids include for example 2-cyclohexenyldithiocarbamic acid, 2-cycloheptenyldithiocarbamic acid, methyldithiocarbamic acid, dimethyldithiocarbamic acid, ethylenebis(dithiocarbamic acid), etc.
Lewis acids include, for example, boron trifluoride, boron trichloride, boron tribromide, aluminum fluoride, aluminum chloride, aluminum bromide, aluminum iodide, aluminum sulfate, iron fluoride, iron chloride, iron bromide, iron nitrate, iron sulfate, gallium fluoride, gallium chloride, antimony fluoride, antimony chloride, antimony sulfte, indium fluoride, indium chloride, tin fluoride, tin chloride, tin bromide, tin iodide, arsenic fluoride, arsenic chloride, zinc fluoride, zinc chloride, zinc bromide, zinc iodide, copper chloride, barium chloride, silver chloride, etc.
It is generally desirable that acids used in the practice of this invention are of such molarity or concentration that they imbue the monomer mix in which they are to be used with a pH of 3 to 8. Preferably, it is less than 7. While the upper end of the pH scale to which the monomer mix could be lowered is slightly alkaline, the addition of acid lowers the pH to point that it would not otherwise reside. In any event, in the case of a monoprotic acid such as HCL, about 0.1 to about 10 weight % of acid is used in the monomer mix. Based on this, the skilled artisan can readily determine equivalent ranges for other acids useful in the practice of this invention.
Making the lenses of this invention is conducted by combining the components of the monomer mix together with the initiators and stabilizers described above according to well known methods of lens formation such as photoinitiated casting in lens molds.
Silicone hydrogels have high oxygen permeability making them particularly desirable for use in the lenses of this invention. When the monomer mix comprises components for the preparation of silicone hydrogels, it is referred to herein as a silicone hydrogel forming mixture. Silicone hydrogels are preferably prepared by polymerizing a mixture containing at least one silicone-containing monomer and at least one hydrophilic monomer. Either the silicone-containing monomer or the hydrophilic monomer may function as a crosslinking agent or a separate crosslinker may be employed. Crosslinking agents are monomers having multiple polymerizable moieties. The term xe2x80x9cmonomerxe2x80x9d when used in this sense refers to a material used in forming the ultimate polymer system The crosslinking agent can be monomeric, dimeric, trimeric, or polymeric molecules and still be considered a monomer with respect to the silicone hydrogel ultimately produced from it. The polymerizable functionalities generally bond to more than one polymer chain creating a network or network-like polymeric structure. There are numerous silicone-containing monomeric units commonly used in the formation of silicone hydrogels. U.S. Pat. Nos. 4,136,250; 4,153,641; 4,740,533; 5,034,461; 5,070,215; 5,260,000; 5,310,779; and 5,358,995 provide some useful examples and each is incorporated herein by reference.
Hydrophilic monomers that have previously been found useful for making silicone hydrogels include: unsaturated carboxylic acids, such as methacrylic and acrylic acids; acrylic substituted alcohols, such as 2-hydroxyethylmethacrylate and 2-hydroxyethylacrylate; vinyl lactams, such as N-vinyl pyrrolidone; and acrylamides, such as methacrylamide and N,N-dimethylacrylamide. Still further examples are the hydrophilic vinyl carbonate or vinyl carbamate monomers disclosed in U.S. Pat. No. 5,070,215, and the hydrophilic oxazolone monomers disclosed in U.S. Pat. No. 4,910,277 and each is incorporated herein by reference.
The preferred components of the monomer mix used to make the silicone hydrogel lenses of this invention include, for example, siloxanes and acrylic/methacrylic acid and derivatives, polyvinyl, typically di- or tri-vinyl monomers, such as di- or tri(meth)acrylates of diethyleneglycol, triethyleneglycol, butyleneglycol and hexane-1,6-diol; divinylbenzene. In the preferred embodiment, the siloxane component is a polydimethyl siloxane. It is combined with a hydrophilic monomer such as hydroxyethyl methacrylate or acrylate derivative. In the most preferred embodiment, the monomers comprise mono-alkyl terminated polydimethylsiloxanes (xe2x80x9cmPDMSxe2x80x9d) such as monomethacryloxy propyl terminated polydimethyl siloxane and a macromer comprising the reaction product of 2-hydroxyethyl methacrylate, methyl methacrylate, methacryloxypropykris(trimethylsiloxy)silane, mono-methacryloxypropyl terminated mono-butyl terminated polydimethylsiloxane, and 3-isopropenyl-xcex1,xcex1-dimethylbenzyl isocyanate. Additionally preferred monomers include, for example, methacryloxypropyl tris(trimethyl siloxy) silane, xe2x80x9cTRISxe2x80x9d; N,N-dimethyl acrylamide, xe2x80x9cDMAxe2x80x9d; triethyleneglycoldimethacrylate, xe2x80x9cTEGDMAxe2x80x9d. Other monomers and crosslinking agents known in the art for making silicone hydrogels can also be used.
The employment of mPDMS is noteworthy as it is thought to be responsible for imbuing the resulting hydrogel with improved mechanical properties such as reduced elastic modulus and tan xcex4 (loss modulus of the material divided by its elastic modulus or Gxe2x80x3/Gxe2x80x2) without compromising monomer compatibility during the polymerization process. Unlike many of the siloxanes predominantly used at present, mPDMS has no polar functionality and is of relatively high molecular weight. Measures to improve its incorporation are thus welcome. The structure of mPDMS can be described as follows: 
where b=0 to 100, and R57 is any C1-10 aliphatic or aromatic group which may include hetero atoms; provided that R57 is not functionalized at the point at which it is bonded to Si. C3-8 alkyl groups are preferred with butyl groups, particularly sec-butyl groups, being most preferred. R56 is any single polymerizable vinyl group. Preferably it is a methacryl moiety but it can also be an acryl or styrenic moiety or other similar moiety.
The monomer mix also includes the initiators and acids described above. These can be added to the mix before, during, or after the mix is combined in a lens mold or other vessel for lens formation.
It is also desirable to carry out the cure in the presence of a diluent. Suitable diluents include alkanols, N,N-dimethylformamide acetamide, acetonitrile, N,N-diethylacetanide, heptane, dimethyl sulfoxide, acetone, tert-butyl acetate, ethyl acetate, isopropyl acetate, and N-methyl-2-pyrrolidone. Low molecular weight (C5-12) akanols are preferred. Dimethyl-3octanol is most preferred.